Niko bought 4 stamps each week for 3 weeks. he wants to put 6 stamps on each page of his album. how many pages will niko use?
tell how you can use tools to solve the problem.
choose a tool to represent the problem. explain why you chose that tool.
solve the problem. explain how you used the tool you chose.

You multiply 4 by 3 because he got 4 stamps each week for 3 weeks. That leads to it being 12 stamps in total. 
He wants 6 stamps out of 12 on each page of his album, so you divide 12 by 6 and get two. 
He will use 2 pages.
The tools used were mathematical reasoning, multiplication and division. 

79 ounces = 2 quarts and 15 ounces.

Explanation:

1) The question is: 1 gallon - (1 quart + 1 pint + 1 ounce)

2) To add and subtract those amounts you have to convert all to one same unit.

3) Since the least unit is ounce, I will convert gallon, quart and pint to ounces.

4) Conversion factors:

1 gallon = 4 quart

1 quart = 2 pints

1 pint = 16 ounces

5) Conversions:

i) 1 gallon × 4 quart / gallon × 2 pint / quart × 16 ounce / pint = 128 ounces

ii) 1 quart × 2 pint / quart × 16 ounce / pint = 32 ounces

iii) 1 pint × 16 ounce / pint = 16ounces

4) Subtract:

1 gallon - (1 quart + 1 pint + 1 ounce) = 128 ounces - (32 ounces + 16 ounces + 1 ounce) = 128 ounces - 49 ounces = 79 ounces ← answer

You can convert it to a mixed number in this way:

79 ounces × 1 quart / 32 ounces = 2. 46875 quarts

0.46875 quarts × 32 ounces / quart = 15 ounces

Then, 79 ounces = 2 quarts and 15 ounces.